GREEN CHEMISTRY AND

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CHAPTER 6

• GREEN CHEMISTRY AND
• ATOM EFFICIENCY

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Chapter Topics

• Definition of Green Chemistry.
• Basic Principles of Green Chemistry.
• Green Chemistry Methodologies.
• - Alternative Feedstocks.
• - Green Solvents.
• - Synthesis Pathways.
• - Inherently Safer Chemistry.
• Case Studies.
• References.

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What is Green Chemistry ?
The design of chemical processes, products and
technologies that reduces or eliminates the use
and generation of hazardous substances
Sources http//center.acs.org/applications/greenc
hem/ http//www.ec.gc.ca/p2progress/2000-2001/en/
sec2_3_2.cfm
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1- Prevention
7 - Use of Renewable Feedstocks
2 - Atom Economy
8 - Reduce Derivatives
3 - Less Hazardous Chemical Syntheses
9 - Catalysis
12 principles
4 - Designing Safer Chemicals
10 - Design for Degradation
5 - Safer Solvents and Auxiliaries
11 - Real-time Analysis for Pollution Prevention
6 - Design for Energy Efficiency
12 - Inherently Safer Chemistry For Accident
Prevention
Source http//www.chemistry.org/portal/a/c/s/1/g
eneral.html?DOCgreenchemistryinstitute\gc_princip
les.html
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Green Chemistry

• The focus area of the EPAs Green Chemistry
  Program considers
• - The use of alternative synthetic pathways
• - The use of alternative reaction conditions
• - The design of safer chemicals that are, for
  example, less toxic than current alternatives or
  inherently safer with regard to accident
  potential.

Source http//www.epa.gov/greenchemistry/docs/g
eneral_fact_sheet.pdf
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An Ideal Chemical Reaction

• Is Simple.
• Is Safe.
• Has a High Yield and Selectivity.
• Is Energy Efficient.
• Uses Renewable and Recyclable Reagents and Raw
  Materials.

Source Green Engineering, Allen and Shonnard,
p. 177
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Brief Overview of Green Chemistry Methodologies
- Alternative Feedstocks. - Green Solvents. -
Synthesis Pathways. - Inherently Safer Chemistry.
Source Green Chemistry, pp. 178
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Feedstock Selection
Always keep in mind the materials -
Persistence, Bioaccumulation and Toxicity. -
Availability and Renewability. - Environmental
Impact during Production (LCA Life Cycle
Management).
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Identifying Alternative Raw Materials in Order to
Improve Environmental Performance

• Innocuous
• Determining the hazards associated with the
  substance (using previously discussed methods) as
  well as alternative pathways if a hazardous
  material needs to be used.

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Identifying Alternative Raw Materials in Order to
Improve Environmental Performance (continued)

• Minimizing Waste Generation
• Determining the quantity of waste produced by the
  given material and alternatives. Also important
  to consider the type of waste and its impact.
• Selective
• Does the selectivity of the substance minimize
  environmental impacts in separation, etc.?
• Efficient
• Offers many benefits... Not only based on yield
  and selectivity. Also consider the atom economy.

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Selection of Feedstocks Basic Guidelines
In surveying the field, it is useful to employ a
taxonomy of methods that develop NGETs. To that
end, we use the seven areas of green chemistry, a
taxonomy that has been laid out to help describe
green chemistry research
A. Use of alternative feedstocks that are both
renewable and less toxic to human health and to
the environment. B. Use of innocuous reagents
that are inherently less hazardous and are
catalytic. C. Employment of natural
processesbiosynthesis, biocatalysis, and
biotech-based chemical transformations for both
efficiency and selectivity.
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D. Use of alternative solvents that reduce
potential harm to the environment and serve as
alternatives to currently used volatile organic
solvents, chlorinated solvents, and other
hazardous chemicals. E. Safer chemical
designwith principles of toxicology to minimize
intrinsic hazards while maintaining needed
functionality. F. Development of alternative
reaction conditions that increase selectivity and
enable easier separations. G. Minimization of
energy consumption.
Source http//www.rand.org/publications/MR/MR1682
/MR1682.ch2.pdf
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Pollutant Chemical Industries Acid Catalysis
and Partial Oxidation
Acid catalysed reactions liquid phase organic
reactions. Problems Reactions are catalysed by
strong Brønstread (H2SO4, HF) and soluble Lewis
(AlCl3, BF3) that are difficult to separate from
the organic product and lead to large volumes of
hazardous waste. Alternative using heterogeneous
catalysis.
Partial Oxidation of organic molecules. Problems
manufacturing methods include toxic and
corrosive chemicals. Ex. processes based on
cobalt- acetic acid- bromide, or using Cr(VI) and
Mn(VII). They produce large volumes of an organic
acid and toxic metal waste. Alternative less
toxic catalytic agents.
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Concerning Pollutant Chemical Industries
A. Energy Production B. Petrochemical
Manufacturing and Processing C. Pulp Paper
Mills D. Chemical Compounds Production E.
Pesticides
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Alternative Reaction Pathway Selection

• Addition ( A B ? AB)
• No waste needs to be treated because the reaction
  is direct.
• Substitution (AB C ? AC B)
• Necessarily generates stoichiometric quantities
  of substances as byproducts and waste that are
  not part of the target molecule.

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Alternative Reaction Pathway Selection (continued)

• Elimination (AB ? A B)
• Does not require other substances, but does
  generate stoichiometric quantities of waste that
  are not part of the final target molecule.

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Example Addition Reactions
The addition of HX to an alkene is an organic
reaction in chemistry where HX, or a halogen
sigma bonded to a hydrogen atom, adds to the
carbon-carbon double bond of an alkene following
Markovnikov's rule (Markovnikov's rule is
observed). The general chemical formula of the
reaction is as follows CC HX
H-C-C-X
Source http//www.encyclopedia4u.com/a/addition-o
f-hx-to-an-alkene.html
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Industrial Addition Processes
Electrophile Source Product Comment
Hydrogen HalideHX Alkyl HalideRX H is electrophile
H2SO4 Alkyl hydrogen sulfate H is electrophile
H2O Alcohol Termed hydrationIn Mild Acid
H2 Alkane Termed hydrogenationRequires palladium or platinum oxid
Mercuric Acetate Alkyl Mercuric AcetateHgOCOOH Converted to alcohol in presence of sodium borohydrate (NaBH4)
Halide(X2) Alkyl dihalide Intermediate is halonium ion (RX)
http//xnet.rrc.mb.ca/martins/Organic203/addition
.htm
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Example Substitution Reactions
In chemistry, Nucleophilic Substitution is a type
of chemical reaction in which one nucleophile
(electron donor) replaces another as a covalent
substituent of some atom. In the examples given
here, the nucleophilic atom is carbon. An
example of nucleophilic substitution is the
hydrolysis of an alkyl bromide, R-Br, under
alkaline conditions, where the "attacking"
nucleophile is hydroxide ion, OH- R-Br OH
R-OH Br- The bromide ion, Br-, is
said to be the leaving group.
Source http//www.encyclopedia4u.com/n/nucleophil
ic-substitution-reaction.html
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Example Elimination Reactions
Halogenoalkanes also undergo Elimination
Reactions in the presence of sodium or potassium
hydroxide.                                        
                  The 2-bromopropane has
reacted to give an alkene - propene. Notice that
a hydrogen atom has been removed from one of the
end carbon atoms together with the bromine from
the centre one. In all simple elimination
reactions the things being removed are on
adjacent carbon atoms, and a double bond is set
up between those carbons.
Source http//www.chemguide.co.uk/mechanisms/eli
m/elimvsubst.htmltop
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Functional Group Approach to Green Chemistry

• Structure Activity Relationship
• Used to determine a potential structural
  modification that may improve the substances
  safety.
• Elimination of Toxic Functional Groups
• Substances in the same functional group tend to
  have the same toxicity. If it is possible,
  eliminate any substances from a given group, or
  mask the toxic substances property rendering it
  safe.

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Functional Group Approach to Green Chemistry

• Reduction of Bioavailability
• Modifying or eliminating certain properties that
  cause toxic substances to be bioavailable.
• Design for Innocuous Fate
• Designing substances to ensure they degrade after
  their useful life.

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Quantitative/Optimization-Based Frameworks for
the Design of Green Chemical Synthesis Pathways
Step 1 select a set of molecular or functional
group building blocks from which a target
molecule can be constructed. Step 2 identify a
series of stoichiometric, thermodynamic, economic
and other constraints that might occur. Step 3
a set of criteria can be used to identify
reaction pathways that deserve further
examination.
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Step 1 Construction of Alternative Chemical
Pathways

• Selection of functional group building blocks
  include the groups
• Present in the product.
• Present in any existing industrial raw materials,
  co -products or by-products.
• Which provide the basic building blocks for the
  functionalities of the product or of similar
  functionalities.
• - Select sets of groups associated with the
  general chemical pathway employed (cyclic,
  acyclic or aromatic).
• - Reject groups that violate property
  restrictions.

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References
EPAs Green Chemistry Program http//www.epa.gov
/greenchemistry/index.html Canada's Green
Chemistry Network http//www.greenchemistry.ca/ G
reen Chemistry Magazine http//www.rsc.org/is/jour
nals/current/green/greenpub.htm Other
References http//www.chemistry.org/portal/a/c/s/1
/acsdisplay.htmlDOCgreenchemistryinstitute\index.
html